The proposed research is designed to develop a new method for characterization of the prefusion elements of embryonic muscle differentiation-the mononucleated myoblasts and their precursors. Previous work in this area has concentrated on describing changes of distinct myoblast populations during normal development and the regulation of some of these changes by the nervous system. The area to be investigated is restricted to development of an experimental system which will allow nerve-dependent myoblast differentiation to occur in tissue culture. It is intended to culture phenotypically pure populations of cloned myoblasts with differentiated neurons and to identify changes in myoblast differentiated state by subsequent clonal analysis of the nerve-influenced cells. If successful, such a system will circumvent the uncontrollable complexity and heterogeneous cellular elements found in developing embryo muscle and will allow precise determination of some of the differentiative steps preceding myoblast fusion.